1. Field of the Invention
The invention relates to continuous processes for the preparation of aluminium nitride by the carbonitriding of alumina using a moving-bed reactor.
2. Discussion of the Prior Art
Processes are known for the continuous preparation of aluminium nitride which use a moving-bed reactor.
In WO 92/16457, it has been proposed to carry out the carbonitriding reaction of alumina in a moving-bed reactor operating with a constant filling rate corresponding to 65-95% of the useful volume of the reactor. This process makes it possible to prepare between 0.5 and 0.8 kg of aluminium nitride granules per hour.
In European Patent Application 0,519,806 it has been proposed to use a methodical reactor operating at a constant filling rate, the length/internal diameter ratio of which is generally between 5 and 20. This process makes it possible to prepare 2.42 kg of aluminium nitride granules per hour.
The major drawback of these technologies resides in the fact that the productivity of this type of reactor remains limited.
One of the ways of increasing the productivity consists in increasing the production of aluminium nitride while keeping the volume of the reactor constant. This generally results in a heterogeneous product, due mainly to an incomplete carbonitriding reaction.
Another way of increasing the productivity consists in decreasing the volume of the reactor while keeping the production constant. Such a volume reduction has the advantage of conserving both a high production and a high homogeneity of the product.